Start-up system for forced flow vapor generator



July 5, 1966 P. H. KOCH 3,259,111

START-UP SYSTEM FOR FORCED FLOW VAPOR GENERATOR Filed June 25, 1964INVENTOR.

Pa ul H. Koch United States Patent 3,259,111 START-UP SYSTEM F03 FGRCEDFLGW VAPUR GENERATOR Paul H. Koch, Akron, ()hio, assignor to TheBabcoclr & Wilcox Company, New York, N.Y., a corporation of New JerseyFiled June 25, 1964, Ser. No. 377,939 2 Claims. (Cl. 122-406) Thisinvention relates in general to the construction and operation of apower plant of the type having a forced flow vapor generator and moreparticularly to a system for starting up a forced flow once-throughvapor generating and superheating unit.

The general object of the present invention is the provision of a systemfor starting up a forced flow vapor generating unit so constructed andarranged as to simplify starting procedure, to minimize the timerequired for starting up, to provide adequate protection of the vaporsuperheating section of the unit and of the turbine. More specifically,the invention is directed to improvements in the construction andoperation of a start-up system of the type described in U.S. Patent No.2,989,038, in which the discharge from the vapor generating section of aoncethrough boiler is passed into a flash chamber or drum, the waterfrom the flash drum is conducted to the inlet end of the vaporgenerating section of the boiler, the vapor from the flash drum ispassed through the vapor superheating section of the boiler and thencondensed for return to the vapor generating section, and provisions aremade for bypassing the flash drum when the working medium is properlyconditioned for rolling and loading the turbine.

In accordance with the present invention, during normal operation of aforced flow vapor generator, vaporizable fluid is successively passedthrough a vapor generating section, a receiver and a superheatingsection to a vapor turbine. The start-up system of the inventioninvolves passing vaporizable fluid under substantial pressure throughthe vapor generating section in indirect heat transfer relation withheating gases, then passing the heated fluid to the receiver whilereducing the pressure of the fluid to cause part of it to flash intovapor, and then separating the vapor portion of the fluid in thereceiver and successively passing it through the superheating sectionand a condensing device for return to the vapor generating section,while recirculating the remaining fluid from the receiver to the vaporgenerating section. The rate of heating gas flow and of vaporizablefluid flow is progressively increased until predetermined conditions offluid temperature and pressure for starting the turbine are attained,then recirculation of fluid from the receiver to the vapor generatingsection and from the superheating section to the vapor generatingsection is discontinued so that all the fluid passes through the vaporgenerating section to the receiver for mixing therein and then passesthrough the superheating section to the turbine. While the loading ofthe turbine is gradually increased, the pressure of the fluid in thereceiver and superheating section is gradually raised to correspond withthe pressure in the vapor generating section. This system permitselimination of much of the conduit and valve work of U.S. Patent No.2,989,- 038, while continuously utilizing the receiver during startingup and normal operation.

In the drawing, I have diagrammatically illustrated a power plantincluding a vapor turbine and a once-through vapor generator, togetherwith apparatus required for starting up and maintaining normal operationof the generator in accordance with the system of the invention.

During normal operation of the power plant system illustrated, feedwaterat a suitable temperature is with- Patented Juiy 5, 1966 drawn by aboiler feed pump 10 from a hot well or feedwater reservoir 12 and forcedunder a substantial positive pressure through tubes forming seriallyconnected vapor generating sections 14 and 16 of a once-through boiler18, with sections 1 and 16 preferably being located mainly in a radiantheat absorbing section of the boiler. Streams of fluid discharging fromvapor generating section 16 are passed through a conduit 20 to a vesselor receiver 22 for mixing therein so that the enthalpy, and thereby thetemperature of the fluid, will be substantially uniform upon dischargefrom the receiver. Conduit 20 contains a pressure reducing valve 21which is normally in a fully open position. After mixing in the receiver22, the fluid is passed through conduits 24 and 26, then successivelypasses through vapor superheating sections 28 and 30, preferably locatedin a convection heat pass of the boiler. Vapor discharging fromsuperheating section 30 passes through conduits 32 and 34 to a vaporturbine 36. Bumers 38 are arranged to supply high-temperature heatinggases to boiler 18 for indirect heat exchange with the fluid flowingthrough the vapor generating and superheating sections. The finalsuperheater outlet temperature is maintained constant by controlling thefiring rate of the burners, and vapor flow to turbine 36 is controlledby a valve 42 contained in conduit 34. The vapor, after passing throughvarious stages of the turbine 36, is condensed in a condenser 44, with apump 45 returning the condensate to the hot well 12 by way of a conduit46.

In a typical start up of the above-described boiler, about one quarterfull load water flow is established through pump 10 and vapor generatingsections 14 and 16 before firing is commenced, with all of such flowpassing through conduit 20 and pressure reducing valve 21 to receiver 22and with valve 21 being positioned to maintain the pressure of the fluidin the vapor generating sections at a high level and to elfect asubstantial reduction in fluid pressure as it passes to receiver 22.Receiver 22 is provided with a drain conduit 48 connected to the returnline 46 and containing a regulating valve 50, with the conduit 48 andvalve 50 being so sized as to permit water outflow from the receiver ata rate corresponding to water inflow to the receiver while maintaining awater level therein, thereby preventing carry-over of water to thesuperheater sections of the unit.

After minimum flow is established, firing is commenced and gastempenature entering the superheater is held to approximately 1000 F. Asthe water temperature increases due to firing, a portion of the waterpassing through the pressure reducing valve 21 will flash into steam dueto the lower pressure at the discharge side of the valve and in thereceiver 22. The remaining water drains from the bottom of receiver 22through conduit 48 for return to hot well 1% by way of conduit 46. Afeedwater supply connection 51, containing a regulating valve 53, opensinto drain line 48.

Steam separated in receiver 22 discharges therefrom through conduits 24and 26, then successively passes through the tubes of superheatersections 28 and 30, cooling the tubes to a safe metal temperature, thenflows to condenser 44 by way of a turbine by-pass line 52, containing acontrol valve 54. Condensate is returned to the hot well 12 through pipe46.

By means of the described arrangement it is possible to restrict thecooling fluid in the vapor generating sections 14 and 16 to water and inthe superheating sections 28 and 30 to vapor. The pressures maintainedin the vapor generating and superheating sections can be suitablyregulated by the valves 21, 42 and 54. During the starting-up period,the pressure maintained in the steam generating sections 14 and 16 willbe substantially higher than the pressure initially in the steamsuperheating sections 28 and 30. Some of the flashed vapor passingthrough the superheating sections can be used for warrning up theturbine during the starting-up period and in that case the valve 42 isbarely opened.

When the quantity and desired conditions of vapor in the turbine by-pass52 are reached, the turbine 36 may be rolled and loaded. To increase theload on the turbine, the pressure in the vessel 22 is raised by openingthe pressure reducing valve 21. As the unit is brought up to pressure,the pressure in the steam generating and superheating sections will tendto approach each other. At some load, about 20% to 30% of full load, thereducing valve 21 will be fully opened, valves 50 and 54 will be closedand valve 42 will be opened. Above this load, flashing in the vessel 22ceases and a water level therein is no longer maintained, with thevessel now serving to mix the fluid passed thereto before discharge tothe vapor superheating section 28.

If it should be desirable to protect the tubes in the vapor superheatingsection during the initial portion of the starting-up period, vapor maybe regulably supplied from an outside source through a pipe 56connected. to pipe 26 and controlled by valve 58.

While in accordance with the provisions of the statutes, I haveillustrated and described herein the best form and mode of operation ofthe invention now known to me, those skilled in the art will understandthat changes may be made in the form of the apparatus disclosed withoutdeparting from the spirit of the invention covered by my claims, andthat certain features of the invention may sometimes be used toadvantage Without a corresponding use of other features.

What is claimed is:

1. The method of starting a power plant system in which, during normaloperation, vaporizable fluid is successively passed through a heatingzone, a receiving zone, and a superheating zone to a vapor turbine, saidmethod comprising passing a vaporizable fluid under a substantialpressure through the heating zone while passing heating gases inindirect heat-transfer relation with the fluid, passing the fluid soheated to the receiving zone while reducing the pressure of the fluid tocause part of it to flash into vapor, effecting separation of the vaporportion of the fluid in the receiving zone and then passing it throughthe superheating zone, while recirculating the remaining fluid from thereceiving zone to the heating zone, condensing the vapor discharge fromthe superheating zone and recirculating it to the heating zone,increasing the rate of heating gas flow and of vaporizable fluid flowthrough said zones until predetermined conditions of fluid temperatureand pressure for starting the turbine are attained, discontinuing therecirculation of fluid from the receiving zone to the heating zone andfrom the superheating zone to the heating zone so that all of the fluidfrom the heating zone passes to the receiving zone for mixing thereinand then passes through the superheating zone to the vapor turbine,while raising the pressure of the fluid in the receiving andsuperheating zones and loading the turbine.

2. The method of starting a power plant system in which, during normaloperation, vaporizable fluid is successively passed through a heatingzone, a receiving zone, and a superheating zone to a vapor turbine, saidmethod Comprising passing a vaporizable fluid under a substantialpressure through the heating zone while passing heating gases inindirect heat-transfer relation with the fluid, passing the fluid soheated to the receiving zone while reducing the pressure of the fluid tocause part of it to flash into vapor, effecting separation of the vaporportion of the fluid in the receiving zone and then passing it throughthe superheating zone, while recirculating the remaining fluid from thereceiving zone to the heating zone, condensing the vapor discharge fromthe superheating zone and recirculating it to the heating zone,progressively increasing the rate of heating gas flow and of vaporizablefluid flow through said zones until predetermined conditions of fluidtemperature and pressure for starting the turbine are attained,discontinuing the recirculation of fluid from the receiving zone to theheating zone and form the superheating zone to the heating zone to thatall of the fluid from the heating zone passes to the receiving zone formixing therein and then passes through the superheating zone to thevapor turbine, while raising the pressure of the fluid in the receivingand superheating zones and gradually loading the turbine.

References Cited by the Examiner UNITED STATES PATENTS 2,989,038 6/1961Schwarz 122-406 3,021,824 2/1962 Profos 122-406 3,102,513 9/1963 Profos122406 CHARLES J. MYHRE, Primary Examiner.

1. THE METHOD OF STARTING A POWER PLANT SYSTEM IN WHICH, DURING NORMALOPERATION, VAPORIZABLE FLUID IS SUCCESSIVELY PASSED THROUGH A HEATINGZONE, A RECEIVING ZONE, AND A SUPERHEATING ZONE TO A VAPOR TURBINE, SAIDMETHOD COMPRISING PASSING A VAPORIZABLE FLUID UNDER A SUBSTANTIALPRESSURE THROUGH THE HEATING ZONE WHILE PASSING HEATING GASES ININDIRECT HEAT-TRANSFER RELATION WITH THE FLUID, PASSING THE FLUID SOHEATED TO THE RECEIVING ZONE WHILE REDUCING THE PRESSURE OF THE FLUID TOCAUSE PART OF IT TO FLASH INTO VAPOR, EFFECTING SEPARATION OF THE VAPORPORTION OF THE FLUID IN THE RECEIVING ZONE AND THEN PASSING IT THROUGHTHE SUPERHEATING ZONE, WHILE RECIRCULATING THE REMAINING FLUID FROM THERECEIVING ZONE TO THE HEATING ZONE, CONDENSING THE VAPOR DISCHARGE FROMTHE SUPERHEATING ZONE AND RECIRCULATING IT TO THE HEATING ZONE,INCREASING THE RATE OF HEATING GAS FLOW AND OF VAPORIZABLE FLUID FLOWTHROUGH SAID ZONES UNTIL PREDETERMINED CONDITIONS OF FLUID TEMPERATUREAND PRESSURE FOR STARTING THE TURBINE ARE ATTAINED, DISCONTINUING THERECIRCULATION OF FLUID FROM THE RECEIVING ZONE TO THE HEATING ZONE ANDFROM THE SUPERHEATING ZONE TO THE HEATING ZONE SO THAT ALL OF THE FLUIDFROM THE HEATING ZONE PASSES TO THE RECEIVING ZONE FOR MIXING THEREINAND THEN PASSES THROUGH THE SUPERHEATING ZONE TO THE VAPOR TURBINE,WHILE RAISING THE PRESSURE OF THE FLUID IN THE RECEIVING ANDSUPERHEATING ZONES AND LOADING THE TURBINE.